Thermostat



E. BLETZ THERMOSTAT June 2l, 1938.

Filed Sept. 5, 1956 .INVENTOR u WITNEssEs;

'mM/w @W fm@ Edward Ze/z.

ATTORNEY Patented June 21, 1938 f UNITED STATES PATENT OFFICE THERMOSTAT Sylvania Application September 5, 1936, Serial No. 99,619

2 Claims.

This invention lrelates to thermostats, and more particularly, to thermostats having a bimetallic disc with a snap action.

It is an object of this invention to so arrange the parts of the thermostat that provision may be made for alarge arcing space and yet, the device as a whole is compact. This provision is particularly adapted to the control of directcurrent circuits, in which the arcing conditions are more severe because the arc is likely to endure longer.

It is a further object of this invention to mount the contact-controlling members on the other face of the main base plate from the blmetalli disc.

It is a further object of this invention to provide means whereby the distance of the bimetallic disc, and simultaneously the distance of the movable contact members from the base plate, may be controlled.

Other objects of the invention and details oi the structure will be apparent from the follow? ing description and the accompanying drawing, in which:

Figure l is a sectional view taken through the center of the thermostat when occupying one position;

Fig. 2 is a view in side elevation showing the thermostat in the opposite position;

Fig. 3 is a top plan view of the base plate;

Fig. 4 ls a similar view of the ring which carries the contact buttons;

Fig. 5 is a plan view of the bimetallic disc;

Fig. 6 is a detailed elevation ci a securing member for the disc; and

Fig. 7 is a side view of the same member.

In the drawing, the base member I is a foundation plate upon which the thermostat is mounted, and is secured in whatever position the thermostat is to be used; It consists of an annular plate having a central opening 2 in which the hub 4 is mounted. The upper surface of the plate I is covered with a layerl of mica or desired insulation 3, which is provided with a central opening to accommodate the hub 4. The central part of the plate I is covered with a supplemental sheet of insulation 5, which is also perforated in the center to accommodate the hub 4. Immediately adjacent the hub 4 is a protective plate 1 which permits the upper end of the hub to be peened over Without injuring the insulation. The hub 4 is threaded and supports a threaded member 8 by means of which a bimetallic disc IU is operatively heldin place .below the plate I.

The underside of the plate I is covered with insulation and a wire or auxiliary heater I2 is embedded in the insulation II to carry a heating current when it is desired to heat the thermostat.

'I'he bimetal disc I Il' is dish-shaped, as shown clearly in Figs. l and 2. Its center is supported by a nut ,|3, by which the center of the disc It is. secured between the threaded member 8 and said nut I3 at the bottom of the member which is threaded into the hub 4. The spindle or member 8 is provided with a stem I5 and a head i5 by which it is manipulated.

Upon the upper face of the base plate I arcuate conducting members I1 to 2| are secured. These members lie with their ends adjacent each other forming the outline of a circle. Any other closed plane ligure would do as well. The end members I1 and 2| of the outline formed by the conducting members are connected to leads 24 which extend to the external circuit which is provided .with direct current by any suitable means. The members I1 to 2| include a member I3, which is in two parts connected by a bridging portion 25 where the member I 8 is laterally deformed to accommodate the passage of a fastening member 21. A hole 28 in the plate I accommodates the member 21.

'I'he member 21 is best shown in Figs. 6 and 7. It consists of a cylindrical rod, the upper portion of which is threaded and the lower portion 29 of which has a rectangular cross section, as best seen by comparing Fig. 6 with Fig. 7. The rectangular end 29 of the lower portion of the rod 21 extends through an opening 30 in the bimetallic disc III. 'Ihe opening 30 is oval, its long dimension being radial of the disc. When the rod 21 is in such position that the long dimension of its head 29 is in line with the radius of the disc, it is readily passed through the opening 30. When the rod is so turned that its head is in a position at right angles to this, it cannot be withdrawn from the disc. There are openings in the insulation, and in the foundation plate I through which the rods 21 are passed, and at their upper end they are threaded into a ring 3| and secured in place by lock nuts 32.

The ring 3| is thus constrainedv to move with the disc III when the disc Ill changes its conguration. The ring 3| carries contact buttons which serve to bridge the gaps between portions I1 to 2|. The contact buttons are .shown in Fig. l at 35, in their circuit-closing position, and are shown `in Fig. 2 in their circuit opening posi' tion. As' best seen at the left of Fig. 1, where Al I) one of these buttons is shown in section, it comprises a button proper 36 which is fastened in place by a rivet 31. The button is countersunk so that it can readily tip. The rivet 31 has on the lower side of the ring 3| a convex washer 38 by which the tilting movement of the button 36 can be accommodated. The convex washer 38 is separated from the ring 3| by .a washer of mica or other insulation 39, and a second washer of insulation at the upper side of the ring co1npletely insulates the button from the ring. The rivet 31 passes through the center of the insulating washers and the hole in the ring 3i which accommodates it is so large that the rivet does not contact the ring.

Upon the underside of the base plate I three stops 40 for limiting the upward snap movement of disc I are secured by means 0i" stems 4I, which pass through the plate I but do not go through the insulation 2. Such a stem is shown at 4| at the left of Fig. 1. The stops lli and their securing stems are indicated at 4| in Fig. 3, but the rods 21 are not shown in this figure. The holes which accommodate the rods 21 are shown at 2B.

In the operation of the device7 considering the parts in the position illustrated in Fig. i, the bridging members or buttons 35 bridge the gaps between the several contact pieces I1 to 2|. Beginning at the contact block l1 and proceeding clockwise in Fig. 3 around the outline of a circle, there is a gap at a stop 4i, then the 'long block I8 passes the pin 21 (represented by the hole '23) and a second gap occurs at the next stop 4 I, after which the block I9 occurs which is connected to theAblock 2|] by the wire I2. This wire affords a bridge around the gap where the second pin 21 occurs. The block is separated from the block 2| by another gap in which a stop 4| occurs.

The blocks I1 and 2| ail'ord terminals to which the leads 2l are connected. The direct-current circuit, which includes the leads 2l, sends a current from the block I1 through the several bridging contacts and block 2| and thence into the circuit including the leads 24. A gap containing a pin 21 lies between blocks 2| and l1 but this is never bridged.

When the device becomes hot, either by the current through the wire I2 heating it or by the surroundings being hot or both, the disc ID because of the unequal expansion of its two layers, reaches a configuration of unstable equilibrium, and then snaps abruptly to the position shown in Fig. 2. In this movement the rods 21 are pushed upward and in consequence, the ring 3| is elevated. This separates the buttons 35 from the conductive members I1 to 2| and breaks the current through the circuit I8.

If this current is heavy, the breaking may be accompanied by an arc across each of the several gaps. When this occurs, it is desirable that the arc shall not act upon the bimetallic disc III, either to heat it or to increase corrosion. This is prevented by the circumstance that the disc Ill is on the other side of the foundation plate I, and because of the several sheets of insulation segregating the region where the arcs form. The ring 3| and consequently, the button' 3l, are moved so far from the conductive members I1 to 2| that the arcs are extinguished.

When the parts cool, the disc lil is strained in the opposite direction and after passing a certain critical temperature, it snaps back to the position illustrated in Pig. l. This movement brings the ring 3| abruptly downward toward the foundation plate l.

In the position shown in Eig. 1, the several buttons 35 bridge the orresponding gaps in the outline i1 to 2|, and in doing so each button tilts about its pivot as much as may be necessary to accommodate itself to the out-of-level position of the ring 3| or to the lack of uniformity in the thicknesses of the parts Il to 2|.

When the device is in the cooled position, r0- tation of the head I6 may cause the threaded member 8 to rise in the hub 4. This will draw the central part of the disc I0 upward but the rods 21, being secured in the holes 3U, prevent the peripheral part oi.' the disc from rising. The curvature of the disc may thereby be increased. If the head i6 is rotated in the opposite direction, the curvature may be lessened because of similar considerations. By this adjustment, the critical operating temperature of the disc may loe predetermined.

When the disc snaps to the open position, it does not move an indefinite distance, but its upper movement is limited by the stops 4|). The points in the disc which abut the stops il! are near, but not at the periphery. When the disc in the position represented by Fig. 2, adjustment oi' the head I6 may cause the disc to change its coniiguration because vits periphery is heid by the stops lli ironi iurther upward movement. Ii the head I6 is turned in the direction to cause the disc to descend, its coniiguration need not thereby he changed because the rods 21 and the ring 3| can descend with it. No eii'ect, except an increased tendency to snap, can occur from rotation of the head IE when the parts are in the Fig. 2 position, but in the Fig. l position, the pressure between the buttons 35 and the contact members I1 to il can be regulated by `turning the head I6.

Variations in the details of construction may be made within the skill of these skilled in the art. The specific illustration and description of one form of the device is not to be considered a limitation. The only intentional limitations are those expressly stated in the claims or necessar ily required by the prior art,

I claim as my invention:

1. In a thermostat, a base plate, a thermally responsive disc adjustably mounted on the base plate at one face thereof, a carrier on the other side of said base plate from said disc, means secured to said disc near the periphery thereof and mechanically securing it to the carrier, conductive members separated by gaps and insulated from, but secured to, the base plate on the face toward the carrier and forming an'outline having adjacent ends, leads united to the end ones of said conductive members, bridging pieces, one for each of the gaps, except the gap separating said end conductive members, said bridging pieces being mounted on, but insulated from, the carrier, the mounting of said disc including means for moving the center thereof to vary its distance from the base plate whereby with the bridging pieces in contact with the conductive members, adjustment of the mounting of the disc will vary the pressure oi the bridging members against the conductive members and also the coniiguration oi' the disc.

2. In a thermostat, a base plate, a thermally responsive disc adiustably mounted on the base plate at one face thereof, a carrier on the other: side of said base plate from said disc, means secured to said disc near the periphery thereof and mechanically securing it to the carrier, conductive members separated by gaps and insulated from but secured to the base plate ou the iaoe toward the carrier, leads united to the end ones of said conductive members, bridging pieces, one for each of the gaps, except the gap separating said end conductive members, said bridging pieces being mounted on, but insulated from, the carrier, the mounting including means for permitting a tilting movement of the bridging pieces relative to the carrier, whereby the bridging pieces will always contact the conductive members fiatly.

' EDWARD BLE'IZ. 

